1. Field of the Invention
The present invention relates to corrosion inhibition. More particularly, the present invention relates to corrosion inhibition in aqueous systems. Still more particularly, the present invention relates to a composition and method for controlling corrosion in aqueous systems.
2. Description of the Prior Art
Numerous chemical additives and combinations of additives have been proposed for inhibiting corrosion in cooling water systems in industrial manufacturing processes, commerical and institutional air conditioning systems, and the like. Among such additives may be mentioned such well known inorganic inhibitors as zinc, chromates, nitrites, nitrates, silicates, benzoates, polyphosphates, among others, all as set out in more detail in "Drew Principles of Industrial Water Treatment" published by Drew Chemical Corporation. Currently, various phosphonic acids and phosphonocarboxylic acids are favored, either alone or in combination with each other, with or without other known corrosion inhibitors.
While all of these known inorganic additives are beneficial to one degree or another in inhibiting corrosion in aqueous systems, there are also drawbacks to the use of some of these. For example, the use of phosphorous-containing additives can degrade, under certain conditions, to form deposits on the metallic surfaces for which protection is being provided, that diminish the effectiveness of the corrosion inhibitor. Some of the known additives, moreover, are environmentally unacceptable. Zinc salts and metal chromates, for instance, are highly toxic to many forms of aquatic life. This creates a disposal problem since discharge of waste water containing such inhibitors into natural waterways is restricted by Federal and State pollution standards and local water quality control standards. The use of polyphosphates also creates an environmental disposal problem because they degrade under certain conditions to orthophosphate which have a nutrient potential for algae growth. The discharge of waste water containing these products is, therefore, also regulated.